Forty-eight rigorously diagnosed outpatient adolescents(16-19) with MDD will enter a single blind two week washout followed by a neuroendocrine challenge with low dose CMI. Patients are then randomly assigned to receive either pulse-load CMI or saline. Patients will be intensively assessed over the next 12 days for therapeutic response without additional pharmacotherapy. The utility of parenteral CMI to predict clinical response to TCA's in adolescent MDD will be evaluated by the protocol.